Detecting sub-system

ABSTRACT

A computerized electricity system for connecting loads to a power source, including: (a) an arc fault detecting sub-system having at least one module including: (i) a relay unit, electrically associated with a particular load, for connecting and disconnecting to a power source; (ii) a current sensor for measuring a current being delivered from the power source to the load, to produce a current measurement; (iii) an analog circuit for receiving the current measurement from the current sensor, and for producing an analog signal based on the current measurement, and a second signal for indicating a potential arc fault event, and (iv) a digital circuit for receiving the second signal from the analog circuit and producing data, and (b) a processing unit connected to each module, so as to receive data corresponding to the analog signal, and the data from the digital circuit, the processing unit for identifying the arc faults, and wherein the processing unit is configured to command the relay unit to disconnect the current in response to identifying the arc faults, and wherein the processing unit is configured to provide this command only if several pre-determined conditions are met, (I) after detection of the potential arc fault event, the current measurement remains substantially unchanged, and (II) after a detection of at least one additional potential arc fault event, the arc fault events are found to be acyclic.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to computerized electricity systems, moreparticularly, to fault detecting systems and methods, and, moreparticularly, to an arc fault detecting system and method.

There are various conditions that may cause an arc fault. Corroded, wornor aged wiring or insulation, worn power cords, old wall outlets withinsufficient contact pressure, electrical stress from repeatedoverloading, etc., may result in an arc fault. These conditions maydamage the insulation of the wiring and create excessive heatingtemperatures. Arc faults may result in a fire depending on variousconditions, such as if combustible materials are in close proximity.

There are also various conditions that may result in a false arc fault.For example, the occurrence of an arc fault in one branch circuit of apower distribution system may generate a false arc in another branchcircuit. As a result, circuit breakers in more than one branch circuitmay erroneously trip. Another example is a relatively noisy load such asan electric drill creating a high frequency disturbance in the circuit,which may appear to be an arc fault.

There are two types of arc faults that may occur in a home. A first typeis a high-energy arc that may be related to high current faults; asecond type is a low current arc that may be related to persistentmomentary contact of electrical conductors. The first type may resultfrom inadvertent connection between a line conductor and neutralconductor or a line conductor and ground. The first type may drawcurrent that is above the rated capacity of the circuit, arcing as thecontacts are physically joined.

The other type of arc fault, the momentary contact of electricalconductors, may be considered more problematic. Since the current in thearc may be limited to less than the trip rating of an associated circuitbreaker, such arcs may become persistent without observation and mayresult in certain conditions. Contact arcs may be caused by springs inswitches that become worn which, in turn, may reduce the forces thathold electrical contacts together. As the electrical contacts heat andcool down, the conductors may touch and separate repeatedly, therebypossibly creating arcs known as “sputtering arcs”.

Contact arcs or sputtering arcs may also be observed in contacts madefrom different materials. For example, aluminum wiring that contactscopper wiring may oxidize at the contact points. In this case, anon-conductive layer may build up over time between the contact pointsand arcing may result. Sputtering arcs may also be observed in extensioncords having insufficient current carrying capacity. As the plug isheated by resistance heating, insulating materials around the contactsmay eventually melt and flow into the contact area, preventing propercontact from being made. The current in the conductors may producemagnetic repulsion forces that push the conductors apart, resulting inan arc. The arc may be extinguished as the current passes through zero.Mechanical or electro-static forces may bring the conductors back intocontact, and the cycle may be repeated.

It is believed that various circuit breakers are not specificallydesigned to guard against sputtering arcs. Special purpose detectorshave been designed to detect sputtering arcs and, when detected, tripthe circuit breakers. Some detectors may depend on the sputtering arcsexceeding a predetermined current or voltage threshold before trippingthe circuit breaker; other detectors are believed to depend on thesputtering arcs having a specific high frequency signature. Still otherdetectors are believed to depend on the sputtering arcs producing awideband high frequency noise ranging from 10 kHz to 1 GHz while the arcis conducting current. These detectors may require that no noise beproduced while the arc is not conducting current, i.e., during the gapsbetween arc conduction. These detectors use various processingtechniques to analyze the repetitive patterns in the noise.

U.S. Pat. No. 6,459,273 discloses a sputtering arc fault detector for asystem having an electrical conductor carrying current to a load. Thesputtering arc fault detector includes a current monitor coupled to theconductor for generating a variable signal responsive to behavior of thecurrent in the conductor. A level detector is coupled to the monitor andgenerates a first pulse when the variable signal exceeds a first level.A step detector is coupled to the monitor and is responsive to rapidstep increases of the variable signal. The step detector generates asecond pulse when the variable signal exceeds a second level. An arcverifier, which is coupled to the level detector and the step detector,combines the first and second pulses, and generates a fault signal whenthe combined pulses exceed a third level.

All of these arc fault detection systems are plagued by false alarms,i.e., the systems identify an arc fault and trigger a current shut-off,in situations in which there is no genuine arc fault, or the arc faultis benign. One example of a benign arc fault is when an additional loadis connected to the circuit. Low quality and/or aging of a switch mayalso cause transient arc-fault type effects in the circuit. Some loadscharacteristically cause the current signal to have arc-fault typeattributes. It must be emphasized that the efficacy of an arc faultdetection system that triggers, in response to a benign arc faultevent—a current shut-off, is greatly compromised, and in manyapplications, the disadvantages of implementing such a system easilyoutweigh the potential benefit.

There is therefore a recognized need for, and it would be highlyadvantageous to have, an arc fault detection system that is robust andreliable, one that triggers current shut-offs in response to genuinearc-fault problems, and identifies and ignores benign arc fault events.

SUMMARY OF THE INVENTION

According to the teachings of the present invention there is provided acomputerized electricity system for connecting loads to at least onepower source, including: (a) an arc fault detecting sub-system fordetecting arc faults, having at least one module including: (i) a relayunit, electrically associated with a particular load, for connecting anddisconnecting to a power source; (ii) a current sensor for measuring acurrent being delivered from the power source to the load, to produce acurrent measurement; (iii) an analog circuit for receiving the currentmeasurement from the current sensor, and for producing an analog signalbased on the current measurement, and a second signal for indicating apotential arc fault event, and (iv) a digital circuit for receiving thesecond signal from the analog circuit and producing data, and (b) aprocessing unit connected to each module, so as to receive datacorresponding to the analog signal, and the data from the digitalcircuit, the processing unit for identifying the arc faults, and whereinthe processing unit is configured to command the relay unit todisconnect the current in response to identifying the arc faults, andwherein the processing unit is configured to provide this command onlyif several pre-determined conditions are met, (I) after detection of thepotential arc fault event, the current measurement remains substantiallyunchanged, and (II) after a detection of at least one additionalpotential arc fault event, the arc fault events are found to be acyclic.

According to further features in the described preferred embodiments,the conditions further include: (III) the potential arc fault event andthe at least one additional potential arc fault event occur within apre-determined amount of time.

According to still further features in the described preferredembodiments, the module is configured to check for a high currentoverload prior to the detecting of the arc faults.

According to still further features in the described preferredembodiments, the module is configured to measure a low current overloadfor a period of at least 20 milliseconds, and to only subsequentlydisconnect the current.

According to still further features in the described preferredembodiments, the computerized system is configured to receive, from auser, an input associated with a particular lag time for disconnectingthe current, and wherein the module is configured to measure a lowcurrent overload over the particular lag time, prior to the currentbeing disconnected.

According to still further features in the described preferredembodiments, the module is configured to check for current leakage priorto the detecting of the arc faults.

According to still further features in the described preferredembodiments, the pre-determined amount of time is at least 0.3 seconds.

According to still further features in the described preferredembodiments, the pre-determined amount of time is at least 1.0 seconds.

According to still further features in the described preferredembodiments, the pre-determined amount of time is at least 3.0 seconds.

According to still further features in the described preferredembodiments, the pre-determined amount of time is a clock cycle of theprocessing unit.

According to still further features in the described preferredembodiments, the computerized electricity system further includes: (c) ameter, associated with the power supply and a voltage sensor, forproviding voltage information to the processing unit.

According to still further features in the described preferredembodiments, the processing unit is configured to utilize the voltageinformation in evaluating the change in load.

According to still further features in the described preferredembodiments, the processing unit is configured to utilize the voltageinformation to neutralize an effect of voltage fluctuation on the changein load.

According to still further features in the described preferredembodiments, the second signal is a digital signal.

According to another aspect of the present invention there is provided acomputerized electricity system for connecting loads to at least onepower source, the computerized electricity system including: an arcfault detecting sub-system for detecting arc faults, the sub-systemincluding: (a) at least one relay unit, electrically associated with aparticular load of the loads, the relay unit for connecting anddisconnecting to a power source of the at least one power source; (b) atleast one current sensor for measuring a current being delivered fromthe power source to the load, so as to produce a current measurement;(c) a processing unit electrically connected to the relay unit and tothe current sensor, the processing unit configured so as to receive asignal corresponding to the current measurement, and wherein theprocessing unit is configured to command the relay unit to disconnectthe current in response to the detecting of the arc faults, and whereinthe processing unit is configured to provide the command only if severalpre-determined conditions are met, the conditions including: (I) afterdetection of the potential arc fault event by the processing unit, usingthe signal, the current measurement is substantially unchanged, and (II)after detection of at least one additional potential arc fault event bythe processing unit, using the signal, the arc fault events are found tooccur in an acyclic fashion.

According to further features in the described preferred embodiments,the conditions further include: (III) the potential arc fault event andthe at least one additional potential arc fault event occur within apre-determined amount of time.

According to still further features in the described preferredembodiments, the processing unit is configured to disconnect the currentafter the current measurement indicates a low current overload for aperiod of at least 20 milliseconds.

According to still further features in the described preferredembodiments, the computerized system is configured to receive, from auser, an input associated with a particular lag time for disconnectingthe current, and wherein the processing unit is configured to disconnectthe current after the current measurement indicates a low currentoverload for the particular lag time.

According to yet another aspect of the present invention there isprovided a computerized electricity system for connecting loads to atleast one power source, the computerized electricity system including:an arc fault detecting sub-system for detecting arc faults, thesub-system including: (a) at least one relay unit, electricallyassociated with a particular load of the loads, the relay unit forconnecting and disconnecting to a power source of the at least one powersource; (b) at least one current sensor for measuring a current beingdelivered from the power source to the load, so as to produce a currentmeasurement; (c) a processing unit electrically connected to the relayunit and to the current sensor, the processing unit configured so as toreceive a signal corresponding to the current measurement, and whereinthe processing unit is configured to command the relay unit todisconnect the current in response to the detecting of the arc faults,and wherein the processing unit is configured to provide the commandonly if several pre-determined conditions are met, the conditionsincluding: (I) after detection of the potential arc fault event by theprocessing unit, using the signal, the current measurement issubstantially unchanged, and (II) after detection of at least oneadditional potential arc fault event by the processing unit, using thesignal, the arc fault events are found to occur within a pre-determinedamount of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice. Throughout thedrawings, like-referenced characters are used to designate likeelements.

In the Drawings:

FIG. 1 is a block diagram of a preferred embodiment of the arc faultdetecting system according to the present invention;

FIG. 2 is a block diagram of a preferred embodiment of an arc faultdetecting method, according to the present invention;

FIG. 3 is a block diagram of a computerized electricity system having anarc fault detecting system, according to the present invention;

FIG. 4 is an exemplary detailed drawing of an analog circuit of thefault detecting system according to the present invention;

FIG. 5 is an exemplary detailed drawing of an arc-fault detectioncircuit within the analog circuit of FIG. 4, according to the presentinvention;

FIG. 6 is an exemplary block diagram of a digital circuit of the faultdetecting system according to the present invention, and

FIG. 7 is a block diagram of a computerized electricity system having anarc fault detecting system, according to another embodiment of thepresent invention, in which the digital circuit is disposed within theprocessing unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a computerized electricity system having an arcfault detecting sub-system and method for operating such a sub-system.

The principles and operation of the arc fault detecting system andmethod according to the present invention may be better understood withreference to the drawings and the accompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawing. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

Referring now to the drawings, FIG. 1 is a block diagram of a preferredembodiment of fault detecting system 100, according to the presentinvention. A plurality of relay units 10, 12, 14 is electricallyconnected to at least one power source 16, and to a plurality ofelectrical loads 20, 22, 24, via current sensors 30, 32, 34. A commonexample of electrical loads 20, 22, 24 is a plurality of householdappliances. Each of current sensors 30, 32, 34 is associated with atleast one of analog circuits 40, 42, 44, which, in turn, are connectedwith at least one of digital circuits 50, 52, 54. Digital circuits 50,52, 54 are connected with a processing unit such as central processingunit (CPU) 60, which controls relay units 10, 12, 14. Associated withCPU 60 is memory 65, which stores data on the past behavior of thecurrent drawn by loads 20, 22, and 24. Preferably, memory 65 stores dataon the current drawn by loads 20, 22, and 24 during the last threecycles. Memory 65 also stores data indicating the current position ofthe various relay units, as well as information corresponding to variouspre-determined operating positions.

Preferably, digital circuits 50, 52, 54 are directly connected to relayunits 10, 12, 14, via electrical lines 70, 72, 74. In the event thateither a low overload, a high overload (short circuit), or leakagecurrent is detected, fault detecting system 100 acts to directly turnoff relay units 10, 12, 14, by means of digital circuits 50, 52, 54,without having to go through the relatively slow CPU 60. In addition,digital circuits 50, 52, 54 provide CPU 60 with digital data indicatingthe current position of the relay units, and the high and low overloadfault status (0 or 1) that CPU 60 processes to determine potential arcfaults.

Analog circuits 40, 42, 44 provide continuous, real-time analog signals80, 82, 84 to CPU 60. These signals correspond to the currentmeasurements of current sensors 30, 32, 34. As will be described ingreater detail hereinbelow, CPU 60 utilizes real-time analog signals 80,82, 84, along with digital data from digital circuits 50, 52, 54, indetermining whether a potential arc fault is indeed an actual arc fault.

It should be emphasized that the analog to digital (A/D) convertingfunction can be performed within CPU 60, or externally to CPU 60, asshown by way of example in FIG. 7.

Each current sensor and corresponding analog circuit, digital circuit,and relay unit, make up a switch device. Thus, switch device 110,includes current sensor 30, analog circuit 40, digital circuit 50, andrelay unit 10.

FIG. 2 is a block diagram of a preferred embodiment of a fault detectingmethod, according to the present invention. Input from the currentsensors is processed in an analog signal processing stage (step 1),preferably by an analog signal processing circuit such as analog circuit40, which will be further described hereinbelow. An output signal fromthe analog signal processing stage is communicated to a digital signalprocessing stage. If either a high overload or a low overload isdetected (step 2), the digital signal processing stage acts todisconnect the current (e.g., by means of relay units such as relayunits 10, 12, 14). As will be described in further detail hereinbelow,if the overload is a low overload, the system can disconnect the currentin a delayed fashion. Similarly, if the leakage current exceeds apre-determined threshold, the digital signal processing stage acts todisconnect the current.

As used herein in the specification and in the claims section thatfollows, the term “potential arc fault event” is meant to exclude a highoverload event. Circuit breakers are typically configured to trip whenthe high overload current reaches five or ten times the nominal currentload (short circuit condition).

In the event that a potential arc fault is identified, but no overload(or leakage current) has been detected, the system does notautomatically disconnect the current. Rather, the processing unit (ordigital circuitry) first determines whether the arcing phenomenon iscyclic (step 3). If so, no disconnection is effected by the system, asthe phenomenon is attributable to the behavior of a particularelectricity consumer (e.g., an appliance). If no cyclic arcing patternis identified, the signal is then compared (step 4) with at least oneprevious signal from the analog signal processing stage, to identifywhether a step change in current has occurred. If so, no disconnectionis effected by the system, as the phenomenon is attributable to anadditional load being connected or disconnected to the circuit.Preferably, the voltage should be monitored, as described hereinbelow,so as to neutralize any fluctuations in voltage from the calculation ofthe step change.

In one preferred embodiment, steps 3 and 4 are effected by a centralprocessing unit such as CPU 60, using digital data from a digital signalprocessing stage. The digital information indicates whether a potentialarc fault has transpired. Prior to controlling and disconnecting therelay unit associated with the arc fault, the CPU checks variouscriteria. Thus, in step 4, the CPU determines whether a change incurrent (typically a step change in current) has occurred, such a changeindicating that a load (e.g., an appliance) has been connected ordisconnected. If such a step change in current has indeed occurred, theCPU attributes the arc event to routine activity, and essentiallyignores the digital information relating to the potential arc fault.

As used herein in the specification and in the claims section thatfollows, the term “no change in current”, “current measurement issubstantially unchanged”, and the like, refers to a current load havingno step change in current. Typically, a step change is indicated if thesystem observes a stable change in current for at least one second, andmore typically, for at least two seconds.

If, however, a (step) change in current has not been observed, the CPUproceeds to determine (step 5) whether the arc event is a recurring arcevent, i.e., that the arc event has occurred a number of times (m)relative to a pre-determined number of times (n) within a pre-determinedtime (t).

If, within t, m<n, the CPU does not disconnect the associated relayunit, but continues to monitor the situation. If, within t, m≧n, the CPUdisconnects the associated relay unit (step 6). Typically, n is aninteger greater or equal to two, and is preferably, at least 3; m is aninteger, and t is greater than 0.30 seconds, preferably greater than 1.0second, and most preferably, at least 3 seconds.

Alternatively, the CPU proceeds to determine (step 5) that the arc eventis a recurring arc event if at least one arc event is determined withina cycle, for at least 2 or 3 successive clock cycles. In this case, thecycle time is greater than 0.30 seconds, preferably greater than 1.0second, and most preferably, at least 3 seconds.

It will be appreciated by one skilled in the art that digital circuitrycan be used to perform steps 3 and/or 4, in lieu of, or in addition to,a CPU. With regard to step 4, both the CPU and such digital circuitryneed to be associated with an analog-to-digital signal converter.

In a preferred embodiment of the present invention, the CPU alsogenerates fault information (step 7) regarding the arc fault. The faultinformation can be used, inter alia, for various diagnostic purposes. Tothis end, it is preferable to store the fault information in a flashmemory, or in another type of memory in which the information isretained when the power is down.

FIG. 3 is a schematic diagram of a preferred embodiment of an inventivecomputerized electricity system (CES) having a fault detectingsub-system for connecting a power source and a load 20, the faultdetecting sub-system including current sensor 30, analog circuit 40,digital circuit 50, relay unit 10, CPU 60 and memory 65. Two-waycommunication lines 110 can be used to receive reports from CPU 60, orto configure CPU 60, e.g., by inputting various parameters.

Various AC sources can be connected to the CES. Thus, by way of example,the CES can be connected to power from the utility company, from agenerator, from a solar system, or from a three-phase network system.The CPU preferably has an algorithm that, along with the relevanttechno-economic data in the memory, enables the CES to select the sourceof energy, depending on availability, cost, etc.

The current and voltage from the AC power sources are monitored bycurrent sensors 75 and voltage sensors 85, which are connected to ameter 80. Meter 80 is connected to CPU 60, which stores the informationin memory and displays and/or sends the information via communicationlines, as requested. The voltage information received from meter 80 isused in evaluating step changes in current, as described hereinabove.

The CES includes current sensors, a first current sensor 30 formeasuring the current flow to the output/appliance and, optionally, asecond current sensor 70 for measuring the leakage current of theoutput. The sensors are connected to analog circuit 40, which tests thesignal against pre-determined thresholds (described in greater detailhereinbelow), and sends an output signal to digital circuit 50. All thedata is transferred to CPU 60 for storing in memory 65 and for furtherprocessing, as needed.

FIG. 4 is an exemplary detailed drawing of an analog circuit 40according to the present invention. Analog circuit 40 is associated withcurrent sensor 30, which is electrically connected to four operationalamplifiers U1A, U1B, U2A, U2B. Between current sensor 30 and theseoperational amplifiers is disposed a matching circuit includingcapacitor C1 and resistor R5, for matching the impedance of currentsensor 30 and operational amplifiers U1A, U1B, U2A, and U2B.

Each pair of operational amplifiers U1A and U1B, U2A and U2B, representsa full sine wave amplifier. Operational amplifiers U1A and U1B amplifythe current wave received from current sensor 30 to a maximum output soas to meet the output requirements of the circuit.

The output of these amplifiers is rectified and then filtered byelements R98 and C59 to make an analog signal to be read by theanalog-to-digital input converter associated with the CPU. The otheroutput of operational amplifiers U1A and U1B is connected to acomparator U1C to determine if a low overload has occurred, and to senda low-overload indication to the digital circuit.

The second pair of operational amplifiers U2A and U2B amplifies thecurrent wave received from current sensor 30 to a maximum output, with alower gain, so as to meet the output requirements of the circuit to meetthe output requirements of the circuit.

The output of operational amplifiers U2A and U2B is directed to ahigh-overload comparator U2C to determine if a high overload hasoccurred, after which an indication of the high-overload event isprovided to the digital circuit.

Analog circuit 40 also includes an arc-fault detection circuit 140according to the present invention. FIG. 5 provides an exemplarydetailed drawing of such an arc-fault detection circuit 140. Arc-faultdetection circuit 140 receives an analog signal from current sensor 30via a matching circuit (both of which are shown in FIG. 4). The signalis directed to an amplifier Q8, a high pass filter C70, and an amplifierQ9. When a potential arc fault is detected, the analog output signalgoes low.

The signal is converted to a digital signal, and is translated as a rawarc-fault detection signal, either by the digital circuit or by the CPU,as described hereinabove. Unlike various prior-art systems, however, thearc-fault detection signal does not automatically trip the relay to shutoff the power. Rather, the signal undergoes analysis, according to thelogical flow diagram of FIG. 2.

FIG. 6 is an exemplary block diagram of a digital circuit 50 of thefault detecting system according to the present invention. Digitalcircuit 50 includes an overload detection circuit 202 having anassociated memory 206, a digital arc detection circuit 204 having anassociated memory 208, a CPU interface 214 for interfacing with CPU 60,and a relay driver 212 for driving relay unit 10 and relay units K1, K2,and K3 (the relay units being schematically illustrated in FIG. 3).

Overload detection circuit 202 preferably receives both high-overloadand low-overload input signals. Preferably, overload detection circuit202 also receives a leakage current input signal from second currentsensor 70. Memory 206 enables overload detection circuit 202 to effect adelayed response to relay driver 212, in the event that a low-overloadinput signal is detected. The delay is preferably at least 20milliseconds, but the magnitude of the delay can be programmed into theCPU according to the specific characteristics of the load. For example,the starting current for a particular air-conditioning unit is 3-5 timesthe nominal current, and the duration of this current is about 10seconds. To prevent tripping of the low overload during the startingperiod, a duration of 10 seconds (or more) can be set as the delayedresponse time for activating relay driver 212, in the event that alow-overload input signal is detected. Preferably, the upper thresholdof the low-overload current can also be programmed into the CPU (e.g.,by means of communication lines 110) according to the specificcharacteristics of the load.

Digital arc-fault detection circuit 204 preferably receives rawarc-fault detection signals from analog arc-fault detection circuit 140(shown in FIGS. 4,5). Preferably, digital arc-fault detection circuit204 also receives an input clock signal, synchronized from the powersource, for comparative purposes in detecting cyclic arc faults. If thearc faults are acyclic, CPU shuts off relay driver.

In the event that a raw arc-fault signal is detected, memory 208 enablesdigital arc-fault detection circuit 204 to effect a delayed input to CPU60 via CPU interface 214.

CPU interface 214 provides CPU 60 with digital information received fromoverload detection circuit 202 and digital arc-fault detection circuit204. For example, if overload detection circuit 202 triggers relaydriver 212, the information is passed on to CPU 60.

CPU interface 214 can also receive a command from CPU 60 to triggerrelay driver 212. For example, and with reference to FIG. 2, if at step5, m≧n, CPU 60 activates relay driver 212, via CPU interface 214, toshut off the appropriate relay unit (e.g., relay unit 10).

Alternatively, digital arc-fault detection circuit 204 can be disposedwithin CPU 60. In this case, CPU interface 214 is not needed. FIG. 7 isa block diagram of a computerized electricity system according to thisembodiment of the present invention, in which the digital circuit isdisposed within CPU 60. The general features of the system shown in FIG.7 are identical to those described with reference to FIG. 1. Digitalcircuits 50, 52, 54 and the requisite functions of analog circuits 50,52, 54, are disposed within CPU 60.

Analog to digital (A/D) converters 90, 92, 94 convert to a digitalsignal, the analog signals from current sensors 30, 32, 34. It will beapparent to one skilled in the art that the (A/D) converting functioncan be effected within CPU 60.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference.

1. A computerized electricity system for connecting loads to at leastone power source, the computerized electricity system comprising: (a) anarc fault detecting sub-system for detecting arc faults, said sub-systemhaving at least one module, each said module including: a relay unit,electrically associated with a particular load of the loads, said relayunit for connecting and disconnecting to a power source of the at leastone power source; (ii) a current sensor for measuring a current beingdelivered from said power source to the load, so as to produce a currentmeasurement; (iii) an analog circuit designed and configured to receivesaid current measurement from said current sensor, and to produce ananalog signal based on said current measurement, and a second signal forindicating a potential arc fault event, and (iv) a digital circuitdesigned and configured to receive said second signal from said analogcircuit, and to produce data, and (b) a processing unit electricallyconnected to each said module of said arc fault detecting sub-system, soas to receive data corresponding to said analog signal, and said datafrom said digital circuit, said processing unit for identifying of saidarc faults, and wherein said processing unit is configured to commandsaid relay unit to disconnect said current in response to saididentifying of said arc faults, and wherein said processing unit isconfigured to provide said command only if several pre-determinedconditions are met, said conditions including: (I) after a detection ofsaid potential arc fault event by said arc fault detecting sub-system,said current measurement remains substantially unchanged, and (II) aftera detection of at least one additional potential arc fault event by saidarc fault detecting sub-system, said arc fault events are found to occurin an acyclic fashion.
 2. The computerized electricity system of claim1, said conditions further including: (III) said potential arc faultevent and said at least one additional potential arc fault event occurwithin a pre-determined amount of time.
 3. The computerized electricitysystem of claim 1, wherein said module is configured to check for a highcurrent overload prior to said detecting of said arc faults.
 4. Thecomputerized electricity system of claim 1, wherein said module isconfigured to measure a low current overload for a period of at least 20milliseconds, and to only subsequently disconnect said current.
 5. Thecomputerized electricity system of claim 1, wherein the computerizedsystem is configured to receive, from a user, an input associated with aparticular lag time for disconnecting said current, and wherein saidmodule is configured to measure a low current overload over saidparticular lag time, prior to said current being disconnected.
 6. Thecomputerized electricity system of claim 1, wherein said module isconfigured to check for current leakage prior to said detecting of saidarc faults.
 7. The computerized electricity system of claim 2, whereinsaid pre-determined amount of time is at least 0.3 seconds.
 8. Thecomputerized electricity system of claim 2, wherein said pre-determinedamount of time is at least 1.0 seconds.
 9. The computerized electricitysystem of claim 2, wherein said pre-determined amount of time is atleast 3.0 seconds.
 10. The computerized electricity system of claim 2,wherein said pre-determined amount of time is a clock cycle of saidprocessing unit.
 11. The computerized electricity system of claim 1,further comprising: (c) a meter, associated with said power supply and avoltage sensor, for providing voltage information to said processingunit.
 12. The computerized electricity system of claim 11, wherein saidprocessing unit is configured to utilize said voltage information inevaluating said change in load.
 13. The computerized electricity systemof claim 11, wherein said processing unit is configured to utilize saidvoltage information to neutralize an effect of voltage fluctuation onsaid change in load.
 14. The computerized electricity system of claim 1,wherein said second signal is a digital signal.
 15. A computerizedelectricity system for connecting loads to at least one power source,the computerized electricity system comprising: an arc fault detectingsub-system for detecting arc faults, said sub-system including: (a) atleast one relay unit, electrically associated with a particular load ofthe loads, said relay unit for connecting and disconnecting to a powersource of the at least one power source; (b) at least one current sensorfor measuring a current being delivered from said power source to theload, so as to produce a current measurement; (c) a processing unitelectrically connected to said relay unit and to said current sensor,said processing unit configured so as to receive a signal correspondingto said current measurement, and wherein said processing unit isconfigured to command said relay unit to disconnect said current inresponse to said detecting of said arc faults, and wherein saidprocessing unit is configured to provide said command only if severalpre-determined conditions are met, said conditions including: (I) afterdetection of said potential arc fault event by said processing unit,using said signal, said current measurement is substantially unchanged,and (II) after detection of at least one additional potential arc faultevent by said processing unit, using said signal, said arc fault eventsare found to occur in an acyclic fashion.
 16. The computerizedelectricity system of claim 15, said conditions further including: (III)said potential arc fault event and said at least one additionalpotential arc fault event occur within a pre-determined amount of time.17. The computerized electricity system of claim 15, wherein saidprocessing unit is configured to disconnect said current after saidcurrent measurement indicates a low current overload for a period of atleast 20 milliseconds.
 18. The computerized electricity system of claim15, wherein the computerized system is configured to receive, from auser, an input associated with a particular lag time for disconnectingsaid current, and wherein said processing unit is configured todisconnect said current after said current measurement indicates a lowcurrent overload for said particular lag time.
 19. A computerizedelectricity system for connecting loads to at least one power source,the computerized electricity system comprising: an arc fault detectingsub-system for detecting arc faults, said sub-system including: (a) atleast one relay unit, electrically associated with a particular load ofthe loads, said relay unit for connecting and disconnecting to a powersource of the at least one power source; (b) at least one current sensorfor measuring a current being delivered from said power source to theload, so as to produce a current measurement; (c) a processing unitelectrically connected to said relay unit and to said current sensor,said processing unit configured so as to receive a signal correspondingto said current measurement, and wherein said processing unit isconfigured to command said relay unit to disconnect said current inresponse to said detecting of said arc faults, and wherein saidprocessing unit is configured to provide said command only if severalpre-determined conditions are met, said conditions including: (I) afterdetection of said potential arc fault event by said processing unit,using said signal, said current measurement is substantially unchanged,and (II) after detection of at least one additional potential arc faultevent by said processing unit, using said signal, said arc fault eventsare found to occur within a pre-determined amount of time.
 20. Thecomputerized electricity system of claim 19, wherein said pre-determinedamount of time is at least 0.3 seconds.